A conventional walk-behind soil compactor includes a frame that carries a generally horizontal compaction plate which is adapted to engage and compact soil or other material. To provide vibratory compacting action, one or more eccentric shafts are journaled for rotation on the frame, and a power source, such as a gasoline engine, is mounted on the frame and the drive shaft of the engine is operably connected to the eccentric shafts to rotate the shafts and provide the vibratory motion.
A walk-behind soil compactor can either be unidirectional, in which the compactor will move only in a single direction over the terrain, or it can be bidirectional or reversible. A typical unidirectional compactor includes a single eccentric shaft, which is normally mounted at the front of the compactor plate, while the engine is mounted adjacent the rear of the plate. With this construction, the rear of the plate, which carries the engine, tends to drag on the ground or terrain, which slows down the travel of the compactor. Moreover, due to the fact that the eccentric shaft is located adjacent the front of the plate, a greater vibrational output occurs at the front of the plate than at the rear, so that the vibratory output is not uniform across the surface area of the compactor plate.
In an attempt to remedy these problems, it has been proposed to mount the eccentric shaft of the unidirectional compactor centrally between the forward and rear ends of the compactor plate. While this construction provides a more uniform vibrational output over the surface area of the compactor plate, it results in a higher profile for the compactor and reduces the speed of travel over the ground.
With a conventional reversible soil compactor, a pair of parallel eccentric shafts are mounted for rotation on the frame, and the drive shaft of the engine is connected to the eccentric shafts through a gear train which is arranged so that the eccentric shafts rotate simultaneously and in opposite directions. To provide forward and rear movement for the compactor, the phase relationship of the weights on the eccentric shafts is changed by a shifting mechanism. The shifting mechanism is very complex, and as it is directly associated with the eccentric shafts, the shifting mechanism is subjected to intense vibration, and therefore has a relatively short service life.
As a further problem, the eccentric shafts are continuously rotating in opposite directions, so that torque generated by one shaft will oppose the torque generated by the second eccentric shaft. Because of this and the weight resulting from the complex shifting mechanism, the speed of travel of the compactor is substantially reduced over a similarly powered unidirectional compactor.
U.S. Pat. No. 5,149,225, is directed to an improved reversible walk-behind vibratory soil compactor in which a reversible clutch is associated with the drive shaft of the engine and selectively connects each eccentric shaft via a drive belt to the drive shaft. The drive belts are arranged so that the eccentric shafts are rotated in opposite directions, but not simultaneously.
Through use of a manual shifting mechanism, the reversible clutch can be shifted between a neutral position, a first engaged position where one of the belts connects the drive shaft to a first of eccentric shafts to rotate that shaft and cause movement of the compactor in a first direction, and a second engaged position, where the other drive belt is connected to the second eccentric shaft to rotate that shaft and cause movement of the compactor in the opposite or reverse direction.
With the construction as described in the aforementioned patent application, only one drive belt is engaged in any instant, so that the torque generated by one eccentric shaft does not oppose or fight the torque generated by the second eccentric shaft, thus enabling the speed of travel to be substantially increased with the same power input.